Liquid crystal esters

ABSTRACT

Liquid crystal substances or compounds of the formula   WHEREIN R is as hereinafter set forth, AS WELL AS COMPOSITIONS AND ELECTRO-OPTICAL APPARATUSES CONTAINING THEM ARE DESCRIBED.

United States Patent 11 1 Ballet et al.

1 1 Dec. 2, 1975 l l LIQUID CRYSTAL ESTERS [75] Inventors: Arthur Boiler, Binningen; I-Ianspeter Scherrer, Therwil, both of 211 Appl. No.: 334,291

[30] Foreign Application Priority Data Feb. 23, 1972 Switzerland 2586/72 Jan. 23, 1973 Switzerland 920/73 [52] 11.8. CI. 260/465 D; 252/299; 260/465 E;

[51] Int. Cl. C07C 121/64 [58] Field of Search 260/465 D [56] 1 References Cited UNITED STATES PATENTS 3,772,389 11/1973 Lowrance. Jr. 260/465 3,790,498 2/1974 Katagiri et a]. 252/299 OTHER PUBLICATIONS Castellano et al. J. Org. Chem, Vol. 33, N0. 9.

Primary Examiner-Lewis Gotts Assistant Examiner-D0lph H. Torrence Attorney, Agent, or Firm-Samuel L. Welt; Bernard S. Leon; William G. Isgro [57] ABSTRACT Liquid crystal substances or compounds of the formula wherein R is as hereinafter set forth,

as well as compositions and electro-optical apparatuses containing them are described.

6 Claims, N0 [Drawings LIQUID CRYSTAL ESTERS BRIEF SUMMARY OF THE INVENTION The invention relates to liquid crystalline esters of the formula wherein R is lower alkyl of 4 to 8 carbon atoms or lower alkoxy of 5 to 8 carbon atoms.

In another aspect, the invention relates to nematic mixtures for electro-optical uses containing the esters of the invention and to the preparation thereof. In still another aspect, the invention relates to dielectrics for electro-optical uses and to the preparation thereof. In yet another aspect, the invention relates to an optical cell comprising as a liquid crystal means one or more esters of the invention.

DETAILED DESCRIPTION OF THE INVENTION The liquid crystalline esters provided by the inven- I tion are compounds of the formula COO CN wherein R is straight-chain alkyl of 4 to 8 carbon atoms or straight-chain alkoxy of 5 to 8 carbon atoms.

The nematic liquid crystal compounds of formula I possess, in the liquid crystalline state, a positive anisotropy of the dielectric constants (ell J. ,ell signifies the dielectric constant along the longitudinal axis of the molecule and EJ. signifies the dielectric constant perpendicular thereto).

In an electric field, the nematic liquid crystals of the invention orient themselves (because 151. with the direction of their largest dielectric constant, (i.e., with their longitudinal axes) parallel to the field direction. This effect is employed, inter alia, in the interaction between embedded molecules and liquid crystalline molecules (guest-host interaction) described by J. H. Heilmeier and L. A. Zanoni [Applied Physics Letters I3, 91 (1968)]. A further interesting application of the dielectric field orientation exists in the rotation cell discovered by M. Schadt and W. Helfrich [Applied Physics Letters 18, I27 (I971 )1.

The eIectro-optical rotation cell of Schadt et al., supra, comprises essentially a condenser having transparent electrodes whose dielectric is formed from a nematic substance or liquid crystal with a dielectric constant of all 61. The longitudinal axes of the molecules of the liquid crystal are arranged in twisted form between the condenser plates in the fieldless state, the twisting structure being defined by the given wall orientation of the molecules. After the application of an electrical potential to the condenser plates, the molecules adjust themselves with their longitudinal axes in the field direction (i.e., perpendicular to the surface of the plates), whereby linear polarized light is no longer rotated in the dielectric (the liquid crystal is uniaxially perpendicular to the surface of the plates). This effect is reversible and canbe used for electrically controlling the optical transmissivity of the condenser.

In such light rotation cells" it is very desirable to utilize compounds as dielectrics which possess a low melting point and slight viscosity. The compounds previously used for this purpose e.g. p-[(p-ethyloxybenzylidene)aminolbenzonitrile have the disadvantage of first showing nematic properties at relatively high temperatures so that electro-optical apparatuses provided with such liquid crystals have to be heated and possibly thermostatted. Further, said compounds possess a high viscosity which, for example, leads to considerable disadvantage in electro-optical apparatuses in that operation thereof requires relatively large voltages and long response times. Unexpectedly, it has now been discovered that the compounds of formula I of the invention possess liquid crystalline properties which correspond to the foregoing requirements. They exhibit not only the necessary large or strong positive anisotropy of the dielectric constants but also individually or in the form of mixtures with one another or with other nematic or non-nematic substances, they are liquid crystalline and exhibit slight viscosity at relatively low temperature. The operation of electro-optical devices is therefore possible with lower voltage and the susceptibility to rearrangement is shorter. An advantage of the compounds of formula I over compounds formerly used for this purpose is their substantially greater stability in view of which they can be handled more conveniently. A further advantage of the compounds of formula I comprises the fact that they form colorless, milky-white nematic phases.

The compounds of formula I are preferably used in the form of mixtures with one another or with other nematic or non-nematic substances. Advantageously, binary or ternary mixtures can be formed. Mixtures whose composition corresponds to a eutectic are especially preferred.

Preferred binary mixtures contain the components in a molar ratio from about I 10 to about I0 I.

More preferred mixtures comprise: p-n-heptylbenzoic acid p'-cyanophenyl ester with p-n-butylbenzoic acid p'-cyanophenyl ester or p-n-pentylbenzoic acid p-cyanophenyl ester in a molar ratio of 2:1 p-n-octylbenzoic acid p-cyanophenyl ester with p-n-butylbenzoic acid p'-cyanophenyl ester or p-n-hexylbenzoic acid p'-cyanophenyl ester in a molar ratio of 2:1; or pn-hexylbenzoic acid p-cyanophenyl ester with p-nbutylbenzoic acid p-cyanophenyl ester in a molar ratio of 2:1.

The compounds of formula I of the invention can be prepared in accordance with the processes hereinafter set forth as follows:

a. reacting a compound of the formula R """COX' II 3 wherein R is as hereinbefore described, and X is a leaving atom or group, with p-hydroxybenzonitrile; or

b. dehydrating a compound of the formula III wherein R is as hereinbefore described; or c. reacting a compound of the formula wherein R is as hereinbefore described, and Y is halogen or arylsulfonyloxy,

with cuprous cyanide or sodium cyanide; or

d. dehydrating a compound of the formula wherein R is as hereinbefore described; or e. diazotizing a compound of the formula wherein R is as hereinbefore described,

and reacting the diaconium salt so obtained with eu= prous cyanide.

. The leaving atom or group denoted by X in formula ll can be halogen, for example, chlorine or bromine, lower alkoxy of l to 7 carbon atoms, preferably rne= thoxy or ethoxy; lower alltanoyloxy of l to 7 carbon atoms, preferably formyloxy or acetoxy; aryl=(lower al= koxy)=, preferably phenyl=(lower alltoxy) of l to 7 car= bon atoms, such as benzyloxy;- aryl=(lower alkanoylosc y)= preferably phenyl=(lowcr alkanoyloxy)= of l to 7 carbon atoms, such as benzoyloxy; lower alkylsul= fonyloxy, preferably mesyloxy; or arylsulfonyloxy, pref= erably tosyloxy.

In process embodiment (a) of the invention, a compound offormula II is reacted with p-hydroxybenzonitrile. The reaction is expedientiy carried out in an inert organic solvent, for example, an ether, such as diethyl ether, tetrahydrofuran or the like, dimethylformamide, benzene, toluene, cyclohexane or carbon tetrachloride.

In the compounds of formula ll, X preferably is halogen, for example, chlorine. in order to bind the hydrogen halide released during the reaction, an acid binding agent is conveniently utilized in the reaction mixture. Suitable acid binding agents comprise tertiary amines, pyridine, or the like. The acid binding agent is preferably present in a large excess so that it can serve simultaneously as a solvent and acid binding agent. The temperature and pressure are not critical aspects of the reaction. However, the reaction is generally carried out at atmospheric pressure and at a temperature in the range of between about room temperature and the boiling temperature of the reaction mixture.

The compounds of formula II wherein X is chlorine can be prepared by reacting a corresponding benzoic acid with thionyl chloride. Thereafter, it is not necessary to isolate the resulting compound of formula I! from the mixture in which it is prepared prior to the reaction with p-hydroxybenzonitrile.

in process embodiment (b) of the invention, a compound of formula III is dehydrated. The dehydration is conveniently carried out using acetic anhydride or anhydrous sodium acetate in glacial acetic acid. The dehydration is carried out at the reflux temperature of the reaction mixture. The pressure is not critical, but the dehydration is advantageously carried out at atmospheric pressure.

The compounds of formula III can be prepared by reacting a compound of formula ll with p-hydroxybenzaldehyde and reacting the resulting ester with hydroxylamine. A compound of formula lll so-obtained need not be isolated from the mixture in which it is prepared, but can be dehydrated in situ.

in process embodiment (c) of the invention, a compound of formula IV is reacted, for example, with cuprous cyanide or sodium cyanide. This reaction is expediently carried out in an inert organic solvent, for example, ethyleneglycol, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, pyridine or acetonitrile. Temperature and pressure are not critical aspects in this reaction. It is expedient to carry out the reaction at atmospheric pressure and at a temperature in the range of between about room temperature and about the I boiling temperature of the reaction mixture.

in the compounds of formula IV, X preferably is halogen, for example, bromine. Such compounds can be prepared, for example, by reacting a compound of formula [l with p=bromophenol. The resulting com pound need not be isolated from the reaction mixture, but can be reacted in situ with cuprous cyanide or so= dium cyanide.

in process embodiment (d) of the invention, a com= pound of formula V is dehydrated. The dehydration can be carried out by boiling a compound of formula V with acetic anhydride in glacial acetic acid or by utiliz= ing phosphorus pentoxide, phosphorus pentachloride, phosphorus oxychloride, thionyl chloride, or the like. The dehydration is preferably carried out in the ab sence of a solvent but can be carried out in a solvent,

for example, benzene, dimethylformamide, pyridine, ethylene dichloride, or the like. The dehydration is ad= vantageously carried out at the reflux temperature of the mixture or the boiling point of the product. Conveniently, the dehydration is carried out at atmospheric pressure or at a reduced pressure.

The compounds of formula V can be prepared by reacting a compound of formula ll with p-hydroxyben- TABLE II Mixture Melting Point Clearing Point p-n-heptylbenzoic acid p-cyanophenyl ester 33% p-n-butylbenzoic acid p-cyanophenyl ester phenyl ester 33% p-n-pentylbenzoic acid p'-cyanophe nyl ester p-n-octylbenzoic acid p'-cyanophenyl ester 33% p-nbutylbenzoic acid p'-cyanophenyl ester p-n-octylbenzoic acid p'-cyanophenyl ester 33% p-mhexylbenzoic acid p' cyanophenyl ester pn-hexylbenzoic acid p-cyanophenyl ester 33% p-n-butylbenzoic acid p-cyanophenyl ester zoic acid, converting the resulting product into an acid chloride and treating this with ammonia. The resulting compound of formula V need not be isolated from the mixture in which it is prepared, but can be dehydrated in situ.

In process embodiment (e) of the invention, a compound of formula VI is utilized as the starting material. It is diazotized and the resulting diazonium salt is subjected to a Sandmeyer reaction. The diazotization is carried out in water at a temperature in the range of from about to C. with the addition of hydrochloric acid and sodium nitrite. The diazonium chloride obtained is then subjected to a Sandmeyer reaction. The latter reaction is conveniently carried out utilizing a solution of, for example, cuprous cyanide or a complex salt thereof. The reaction is carried out at a temperature in the range of between about 0C. and about 100C, preferably in the range of from about 70 to about 80C. Pressure is not critical, but the reaction is advantageously carried out at atmospheric pressure.

The compounds of formula VI can be prepared by reacting a compound of formula II with N-benzylidenep-hydroxyaniline and subsequent cleavage of the resulting Schiffs base with an aqueous mineral acid.

The physical properties of the nematic compounds of formula I provided by the invention are set forth in the following Table I:

*monotrope clearing point The compounds of formula I can also be used in the form of mixtures with other nematic or non-nematic substances, for example, with Schiffs bases of the formula R' CN VII wherein R is striaght-chain lower alkyl of 2 to 8 carbon atoms, straight-chain lower alkoxy of 4 to 7 carbon atoms, or straight-chain lower alkanoyloxy of 2 to 8 carbon atoms.

The Schiffs bases of formula VII wherein R is a straight-chain lower alkyl of 2 to 8 carbon atoms are new and can be prepared, for example, by reacting a compound of the formula VIII EXAMPLE 1 Preparation of pn-butylbenzoic acid p-cyanophenyl ester 5.6 g. of p-n-butylbenzoic acid chloride in 12 ml. of

absolute benzene are added to 3.1 g. of p-hydroxybenzonitrile in 25 ml. of absolute pyridine. The mixture is stirred overnight at room temperature and subsequently for an additional 2 hours at 50C. After cooling, the mixture is extracted with ether and the extract washed with dilute hydrochloric acid and water, whereby there are finally obtained 9 g. of crude p-nbutylbenzoic acid p-cyanophenyl ester. This product is dissolved in toluene and chromatographed on 250 g. of silica gel. From the uniform fraction on the thin-layer there are obtained, after recrystallization from hexane, 4 g. of p-n-butylbenzoic acid p-cyano'phenyl ester, having a melting point of 67C. and a monotrope clearing point of 415C. The nuclear magnetic resonance and infrared spectra correspond to the expected structure.

The starting material, i.e., p-n-butylbenzoic acid chloride, can be prepared as follows:

50 g. of p-n-butylbenzoic acid are dissolved in 150 ml. of thionyl chloride, and the mixture is boiled at reflux for 1 hour. The excess thionyl chloride is then removed at normal pressure and the p-n-butylbenzoic acid chloride distilled under a high vacuum. The obtained p-n-butylbenzoic acid chloride has a boiling point of 100 105C/25 mm.

EXAMPLE 2 Preparation of pn-pentylbenzoic acid p'-cyanophenyl ester 3.1 g. of p-hydroxybenzonitrile are dissolved in 40 ml. of absolute pyridine. Then 6 g. of p-n-pentylbenzoic acid chloride in 20 ml. of benzene are added dropwise at room temperature and the mixture is subsequently stirred overnight. After warming for a short period, the mixture is worked up as described in Example 1, whereby there are obtained 7.5 g. of crude ester. The latter is chromatographed on silica gel using toluenelacetone (19:1). From the uniform fraction there are obtained, after recrystallization from hexane, 2.6 g. of p-n-pentylbenzoic acid p-cyanophenyl ester having a melting point of 605C. and a monotrope clearing point of 565C.

The starting material, i.e., p-n-pentylbenzoic acid chloride, can be prepared as follows:

g. of p-n-pentylbenzoic acid are dissolved in 100 ml. of thionyl chloride, and the mixture is boiled at reflux for 1 hour. The excess thionyl chloride is then re moved by distillation and the desired acid chloride dis tilled under a high vacuum. The obtained p-n-pentylbenzoic acid chloride has a boiling point of 104C/2 EXAMPLE-3 Preparation of p-n-hexylbenzoic acid p-cyanophenyl ester 1.4 g. of p-hydroxybenzonitrile in 25 ml. of absolute pyridine and 2.9 g. of p-n-hexylbenzoic acid chloride in 12 ml. of absolute benzene are mixed together, stirred overnight at room temperature and subsequently for an additional 2 hours at 50C. The cooled reaction mixture is poured on to ice-water and then extracted with ether. The mixture is washed with dilute hydrochloric acid, dilute sodium hydroxide and finally with water until neutral. After drying and concentration of the solution, there are obtained 3.7 g. of crude product. Said product is chromatographed on silica gel using toluenelacetone (19:1 whereby there are finally obtained 1.4 g. of p-n-hexylbenzoic acid p-cyanophenyl ester having a melting point of 45C. and a clearing point of 48C.

The starting material, i.e., p-n-hexylbenzoic acid chloride, can be prepared as follows:

9.4 g. of p-n-hexylbenzoic acid and 50 ml. of thionyl chloride are mixed together and warmed for 1 hour at C. The excess thionyl chloride is then removed by distillation at normal pressure and the p-n-hexylbenzoic acid chloride is removed by distillation under a high vacuum. The obtained p-n-hexylbenzoic acid chloride has a boiling point of l10C/0.05 mm.

EXAMPLE 4 Preparation of p-n-heptylbenzoic acid p-cyanophenyl ester 6.6 g. of p-n-heptylbenzoic acid chloride are dissolved in 25 ml. of absolute benzene and added dropwise to 3 g. of p-hydroxybenzonitrile in 50 ml. of absolute pyridine. The reaction mixture is stirred overnight at room temperature and then for an additional 2 hours at 50C. After cooling, ice-water is added and the product is extracted with ether. The ether extract is washed with dilute hydrochloric acid, dilute sodium hydroxide and water, whereby there are finally obtained 7.6 g. of crude pn-heptylbenzoic acid p-cyanophenyl ester. This product is chromatographed on 300 g. of silica gel and eluted with hexane/ether (4:1 After recrystallization from hexane, 6.0 g. of the desired p-n-heptylbenzoic acid pcyanophenyl ester are obtained, having a melting point of 44C. and a clearing point of 565C.

The starting material, i.e., p-n-heptylbenzoic acid chloride, can be prepared as follows:

15 g. of p-n-heptylbenzoic acid and ml. of thionyl chloride are boiled at reflux until the evolution of gas has terminated. The excess thionyl chloride is then removed by distillation at normal pressure and the p-nheptylbenzoic acid chloride is distilled under a high vacuum, whereby 13.2 g. of p-n-heptylbenzoic acid chloride, having a boiling point of l65167C./5mm. are obtained.

EXAMPLE 5 Preparation of p-n-octylbenzoic acid p'-cyanophenyl ester 7 g. of p-n-octylbenzoic acid chloride in 25 ml. of absolute benzene are added dropwise to 3 g. of p-hydroxybenzonitrile in 50 ml. of absolute pyridine. The mixture is then stirred overnight at room temperature and for an additional 2 hours at 50C. The reaction mixture is poured on to ice-water and the product isolated as described in Example 4. 8.7 g. of crude ester are chromatographed on silica gel using benzene. After recrystallization from hexane, there are obtained 5.2 g. of pure p-n-octylbenzoic acid p'-cyanophenyl ester having a melting point of 465C. and a clearing point of 53.5C.

The starting material, i.e., p-n-octylbenzoic acid chloride, can be prepared as follows:

20 g. of p-n-octylbenzoic acid and 100 ml. of thionyl chloride are boiled at reflux for 1 hour. The excess thionyl chloride is removed by distillation at normal pres- 9 sure. The residue is mixed with absolute toluene and concentrated under vacuum. The obtained crude p-n- 'octylbenzoic acid chloride can be used without further purification.

EXAMPLE 6 Preparation of p-n-butylbenzoic acid p-cyanophenyl ester 4.5 g. of p-hydroxybenzaldehyde are dissolved in 50 ml. of pyridine. 8 g. of p-n-butylbenzoic acid chloride in 25 ml. of benzene are added dropwise thereto at room temperature. The mixture is stirred overnight at room temperature and subsequently for an additional 2 hours at 50C. The mixture is then poured on to icewater and extracted with ether. The ether extract is washed with water, dilute hydrochloric acid and water, whereby there are finally obtained, after drying and concentration of the solution, 10.2 g. of crude p-nbutylbenzoic acid p-cyanphenyl ester. 8.2 g. of the crystalline ester are obtained after recrystallization from ether/hexane. 8 g. of this ester are boiled at reflux for 16 hours with 2.85 g. of hydroxylamine hydrochloride and 4.5 g. of anhydrous sodium acetate in 100 ml. of glacial acetic acid. The mixture is cooled, the major portion of glacial acetic acid is removed by distillation under vacuum, water added to the residue and the product extracted with ether. From the ether extract there are obtained, after washing with water and drying with sodium sulfate, 7.0 g. of crude product. This product is chromatographed on silica gel using benzene. From the uniform fractions there is obtained, after recrystallization from hexane, p-n-butylbenzoic acid p'- cyanophenyl ester which is identical with that obtained in Example 1.

EXAMPLE 7 Preparation of p-n-octylbenzoic acid p'-cyanophenyl ester 3.7 g. of p-n-octylbenzoic acid p'-bromophenyl ester are boiled at reflux with 1.1 g. of cuprous cyanide in 5 ml. of dimethylformamide. The reaction mixture is then poured on to 2 ml. of ethylenediamine and 6 m1. of water, shaken vigorously for 5 minutes and then extracted twice with benzene. The organic extracts are washed again with ethylenediamine in water and then several times with water. There are obtained 1.9 g. of crystalline crude product still containing a small amount of starting material which is then separated by chromatography on silica gel using toluene. The p-noctylbenzoic acid p'-cyanophenyl ester obtained after recrystallization has a melting point of 465C. and a clearing point of 54C. and is identical with the product obtained in Example 5.

The starting material, i.e., p-n-octylbenzoic acid pbromophenyl ester, can be prepared as follows:

4.5 g. of p-bromophenol are dissolved in 50 ml. of absolute pyridine and mixed with 7 g. of p-n-octylbenzoic acid chloride in 25 ml. of absolute benzene. The mixture is subsequently stirred overnight at room temperature and then poured into ice-water and extracted with ether. The organic phase is washed with dilute hydrochloric acid, dilute sodium hydroxide and water, dried over sodium sulfate and concentrated, whereby there are obtained 8.4 g. of p-n-octylbenzoic acid pbromophenyl ester which is practically pure on thinlayer.

10 EXAMPLE 8 Preparation of p-n-hexyloxybenzoic acid p-cyanophen yl ester 2 g. of p-hydroxybenzonitrile are dissolved in 5 ml. of absolute pyridine. A solution of 4 g. of p-n-hexyloxybenzoic acid chloride in 2 ml. of absolute benzene is added at room temperature to the resulting solution. The mixture is stirred overnight at room temperature, then taken up in ether and the ether phase washed successively with dilute hydrochloric acid, dilute sodium hydroxide and distilled water. After drying and concentration, there are obtained 4.9 g. of crude product which is recrystallized twice from ethanol to yield 4.3 g. of p-n-hexyloxybenzoic acid p-cyanophenyl ester having a melting point of 71C. and a clearing point of 82C.

The p-n-hexyloxybenzoic acid chloride starting material can be prepared by boiling p-n-hexyloxybenzoic acid with thionyl chloride followed by distillation at 130C/0.1 mm.

The following Example illustrates the preparation of a Schiffs base of formula Vll:

EXAMPLE A Preparation of p-[(p-ethylbenzyliden)amino]benzonitrile A mixture of 5.9 g. of p-aminobenzonitrile and 6.7 g. of p-ethylbenzaldehyde is gassed with nitrogen in ml. of benzene after the addition of 150 mg. of p-to1 uenesulfonic acid and the mixture is heated at reflux for 1 hour (bath temperature C.) The water formed is removed by means of a water separator. During an additional hour, the benzene which condensed in the reflux condenser is led back into the reaction vessel via a layer of 50 g. of aluminum oxide (activity 1). After cooling, 2 g. of solid potassium carbonate are added. Then, the mixture is filtered and the filtrate freed from a solvent under vacuum at 50C. (bath temperature), whereby there remains 11.5 g. of a yellow oil which crystallizes upon cooling. Purification is carried out by several recrystallizations from isopropanol to a constant melting point and until by-products can no longer be observed by gas chromatogram. The pure p-[(pethylbenzyliden)-amino]benzonitrile melts at 76.277.0C. and is liquid crystalline upon cooling to 63.059.7C.; U.V. (ethanol); e 25800 (shoulder at 316 nm). The nuclear magnetic resonance, mass spectrum, infrared and microanalysis confirm the structure of the product.

We claim:

1. A compound of the formula R CO CN wherein R is straight-chain lower alkyl of 4 to 8 carbon atoms.

2. A compound in accordance with claim 1, p-nbutylbenzoic acid p'-cyanophenyl ester.

3. A compound in accordance with claim 1, p-n-pentylbenzoic acid p-cyanophenyl ester.

4. A compound in accordance with claim 1, p-n-hexylbenzoic acid p'-cyanophenyl ester.

5. A compound in accordance with claim 1, p-n-heptylbenzoic acid p'-cyanophenyl ester.

6. A compound in accordance with claim 1, p-noctylbenzoic acid p'-cyanophenyl ester. 

1. A COMPOUND OF THE FORMULA
 2. A compound in accordance with claim 1, p-n-butylbenzoic acid p''-cyanophenyl ester.
 3. A compound in accordance with claim 1, p-n-pentylbenzoic acid p''-cyanophenyl ester.
 4. A compound in accordance with claim 1, p-n-hexylbenzoic acid p''-cyanophenyl ester.
 5. A compound in accordance with claim 1, p-n-heptylbenzoic acid p''-cyanophenyl ester.
 6. A compound in accordance with claim 1, p-n-octylbenzoic acid p''-cyanophenyl ester. 